This invention relates to tissue treatment systems, specifically to non-invasive tissue oxygenation systems for accelerating the healing of damaged tissue and promoting tissue viability. When skin is damaged a wound results and a four phase healing process begins. Optimal metabolic function of these cells to repopulate the wound requires that oxygen be available for all phases of wound healing. The more layers of tissue that are damaged the greater the risk for complications to occur in the wound healing process.
Difficult-to-heal wounds encounter barriers to the wound healing process and typically experience delays in one or more of the last three phases of wound healing. One of the most common contributing factors to venous leg ulcers, diabetic foot ulcers and pressure ulcers experiencing delays in the healing process is the problem of chronic wound ischemia. Chronic wound ischemia a pathological condition that restricts blood supply, oxygen delivery and blood request for adequate oxygenation of tissue, inhibiting normal wound healing.
In practice the standard of care for treating difficult-to-heal wounds typically involves the use of an advanced wound dressing or combination of advanced wound dressings providing a dressing treatment system. An advanced dressing is positioned on the wound site or on the wound site and the surrounding intact skin providing a wound site enclosure. An advanced wound dressing is typically comprised of materials having properties for promoting moist wound healing, managing wound exudate and helping control wound bioburden. The typical material components in combination further include properties for providing limited moisture vapor permeability. The lower the dressing's moisture vapor permeability or more occlusive the dressing the lower the amount of ambient air and the respective lower amount of oxygen is thereby available to the wound bed. 100% oxygen exerts a partial pressure of 760 mm Hg. Ambient air is comprised of about 21% oxygen thereby exerting a partial pressure of oxygen at about 159 mm Hg. A typical advanced wound dressing or wound dressing system comprised of lower moisture vapor permeable materials impacts the available oxygen for the wound site thereby limiting the partial pressure of oxygen at the enclosed wounds site at about 10 mm Hg to 60 mm Hg. Fresh air is provided to the wound site only when the dressing is changed. A dressing may remain covering the wound site for up to seven days before a dressing change is required. The moisture vapor permeability property of an advanced wound dressing providing a reduced oxygen wound environment thereby works against the optimal metabolic function of cells to repopulate the wound which requires that oxygen be available for all phases of wound healing.
Prior art methods of tissue oxygenation for difficult-to-heal wounds include topical hyperbaric oxygen applied intermittently or continuously. Intermittent topical hyperbaric oxygen is a method of tissue oxygenation comprising of a sealed extremity or partial body chamber and a connected source of high flow pure oxygen whereby the affected limb or affected body area is positioned in a sealed extremity chamber or partial body chamber so that the oxygen source supplying the chamber is providing the patient topically up to 100% oxygen at flow rates that may exceed 300 liters per hour pressurizing the interior of the chamber up to 1.05% normal atmospheric pressure thereby increasing the available oxygen for cellular processing at affected wound site. During the oxygen application, the partial pressure of oxygen exerted inside the topical or partial body chamber may attain 798 mm Hg. Topical hyperbaric oxygen is applied for about 90 minutes. Prior art also teaches a plurality of methods to apply topically hyperbaric oxygen intermittently. A partial body chamber for treating sacral wounds has been described in U.S. Pat. No. 4,328,799 to LoPiano (1980) whereby oxygen is applied from a stationary supply tank into the interior of the chamber through connected tubing. A similar method of applying topical hyperbaric oxygen is described in U.S. Pat. No. 5,478,310 to Dyson-Cantwell (1995) whereby oxygen is applied from a stationary supply tank into the interior of the disposable extremity chamber through connected tubing. These and similar methods of applying intermittent topical hyperbaric oxygen are restrictive, cumbersome, can only supply oxygen to the affected area intermittently with no systemic application, and can only be applied with a minimal increase in atmospheric pressure (about 5%). Therefore the effect of the oxygen therapy on the wound can be minimal which is evidenced by the lack of commercial success from topical hyperbaric oxygen extremity chambers.
Both U.S. Pat. No. 5,578,022 to Scherson (1996) and U.S. Pat. No. 5,788,682 to Maget (1998) describe disposable devices utilizing transmission of gases in ionic form through ion specific membranes to apply supplemental oxygen directly to the wound bed. These devices are described as battery powered, disposable, oxygen producing bandages and methods that are applied directly over the wound. They both include electrochemical oxygen generation using variations of the same 4 electron formula originally developed for NASA in U.S. Pat. No. 3,489,670 to Maget (1970). The amount of oxygen that can be applied to the wound is typically 3 milliliters per hour. Specific oxygen flow rates are generated by means of corresponding specific, preselected battery sizes and specific prescribed amperages. Prior art describes disposable devices are either “on or off.” The prior art describes disposable devices without means to sense temperature changes in the wound site oxygen environment. Prior art does not provide a means to deliver a varying (adjustable) oxygen flow rate without requiring the patient to obtain and apply a new device with a new battery having a specific amperage. Additional limitations are also associated with the use of a fixed non-variable oxygen flow rate.
No prior art low dose tissue oxygenation device provides continuous oxygen adjustability to a patient's wound(s) creating a controlled hyperoxia and hypoxia wound environment for damaged tissue to accelerate wound healing and promote tissue viability. Specifically, nothing in the prior art teaches continuous oxygen adjustability based on actual flow rate, partial pressures at the wound site, and temperatures at the wound site.